Speed programmed friction welder

ABSTRACT

A friction welding machine of the kind in which two workpieces are rotated in rubbing contact at a common interface to develop weld heat by friction and plastic working includes a variable speed drive for rotating one workpiece with respect to the other to produce the rubbing contact and a programmer for generating a desired speed signal and a controller for producing an actual speed in accordance with the desired speed.

United States Patent Inventors Appl. No.

Filed Patented Assignee SPEED PROGRAMME!) FRICTION WELDER [561References Cited UNITED STATES PATENTS 3.162.068 12/1964 Hardy 78/823,234,647 2/1966 Hollander et al. 29/4703 3.235.160 2/1966 Walton 228/23273233 9/ l 966 Oberle et al .1 29/4703 3,455,494 7/1969 Stamm 228/2Primary Examiner-John F. Campbell Assistant Examiner-R. J CraigAtt0rneyFryer, Tjensvold, Feix, Phillips and Lempio 15 Claims, 22Drawing Figs.

U.S. Cl. 228/2, 1 29/4703, 78/82, 156/73 Int. Cl 823k 27/00 Field ofSearch 228/2; 78/82; 29/4703; 156/73 CONTROL COMMAND PATENTEI] JUL 6'9?!SHEET 01 [If INVENTORS. G. FARMER MULLER LOBERLE CHARLES CA\ \/\N LOYDROBERT G. THEODORE 1 2 ATTORNE 5 SHEET 02 0F f0 mm x l aw 1G. 1 m I L zM 7 \A H 0 \Z 8 .E a T. x12 f 7W1 W A Q 2 I\ Q 0 m L 9 I Z CAL.V\N D.LOYD ROBERT Gr, NHLLER THEODORE; LOBERLE.

J yy w +P ATTORNE z CiRCUlT PATENTEU JUL BIB?! I 3,591,068

SHEH 03 0F 11 CONTROL COMMAND INVENTORS. CHARLES GK FARMER CALWN D. LOYDROBERT CI. MILLER BY THEODORE L. OBERLE.

PATENTEDJUL 6197i 3,591,068

Ez -EA- R.F?M.(ACTUAL) PRESSURE TIME (SEC) .R.P.M.(DES1RED) ENERGYHORSEFOWER TIME (SEC) INVENTORS. CHARLES CT. FARMER CALVIN D. LOYDROBERT G. NHLLER BY THEODORE L. OBl-LRLE.

PATENTEDJUL slsn 3.591.068

sum 05 [1F 11 RP. M. (ACTUAL) PRESSURE TORQUE TIME (SEC) RP. M. (DESIRED) HORSE POWER ENERGY TIME (SEC) INVENTORS. CHARLES Cr. FARMER C,Al v\ND. LOYD ROBERT Cr. M\\ F R BY THEODORE L. OBERLE.

PATENTED JUL 6 I9?! SHEET 08 0F 11 v /RPM.(ACTUAL) WW PRESSURE TORQUE .2.3 .4 .5 .6 .7 .8 |:O l IE2 {3 1:4

TIME (SEC) E: E EB /R.P.M.(DES|RED) HORSE POWER ENERGY .2 3 .4 .5 .6 ."7.8 .9 IfO U [.2 I3 [4 TIME (SEC) INVENTORS. CHARLES G. FARMER CALVlN DLovo ROBERT Gr. M ILLER BY THEODORE L OBERLE PATENTEDJUL 61971 3.591.068

SHEET 07111 11 E :5 -EA RPM. (ACTUAL) PRESSURE TORQUE TIME (55c)HORSEPOWER ENERGY TIME (SEC) mvm'roras. CHARLES C1. FARMER CALVIN D.LOYD ROBERT C: M1LLF R BY THEODORE L. OBERLE PATENTEIJJIII SIS?!3,591,068 SHEET near 11 E:. -lU A- R.RIvI.(AcTuAL) C5 C5 PRESSURE .I .2.3 .4 .5 .6 .7 .8 Io I. I I2 I3 I4 I5 TIME (SEC) E15 -lU E1- R.P. M.(DESIRED) ENERGY .I .2 .3'. .4 .5 .'6 i .8 .9 I0 ITI I I3 I4 I5 TIME(SEC) INVENT IRS. CHARLES G. FARMER CALVIN D- LOYD ROBERT Cxv MILLERTHEODORL L. OBERLE PATENTEUJUL 6:97:

SHEET 10 0F 11 E.:'. -lE

TIME

TIME

KUZU

FORGING RANGE TIME TIME

INVENTORS. CHARLES C; FARMER CALVIN D. LOY ROBERT CT- MILLER THEODORE L.OBERLL SPEED PROGRAMMED FRICTION WELDER This application is a divisionof Ser. No. 568,920 filed July 29, 1966 and now U.S. Pat. No. 3,462,826granted Aug. 26, 1969.

This application relates to a welding process of the general kind inwhich end surfaces of two parts to be welded are pressed together inrotating rubbingcontact at a common interface to heat the interface to aplastic weldable condition. This invention relates particularly to amethod for controlling the rotational speed to produce any predeterminedprogram of speed variation with time during the entire period the partsare engaged in rotating rubbing contact.

The welding process of the general kind noted above has developed as twoseparate techniques, conventional friction welding and inertial welding.

Conventional friction welding has been described in considerable detailin Russian and Czechoslovakian technical publications dating back to1957. In the conventional friction welding process the end of one partto be welded is rotated against an end of the other part at a relativelyconstant speed and under a relatively constant load until the interfaceis heated to a'plastic condition. The relative rotation is then rapidlystopped. Quite often the load is increased as rotation is stopped tocompact the weld zone and to squeeze out impurities.

In the inertial process a control weight is connected for rotation withone of the parts to be welded. The weight is accelerated to a selectedrotational speed to store a predetermined amount of energy before theparts are engaged. The parts are then pressed together under a desiredload while the inertial energy stored in the weight is expended inheating and working the interface. The rotational speed of the inertialweight continuously decreases, and the entire energy of the inertialweight is preferably expended in welding the parts. This inertialprocess has numerous advantages over the conventional friction weldingprocess. These advantages are discussed in detail in U.S. applicationSer. No. 407,955 filed Oct. 27, 1964 and assigned to the same assigneeas the present invention. In brief summary, it may be noted that theinertial process provides two main advantages over the conventionalfriction welding process. The inertial process is much quicker andproduces much more plastic working at low speeds. These two advantagescombined to produce high quality welds.

Neither the conventional friction welding process nor the inertialprocess has provided for continuous control, or modification, of theprocess characteristics during the time that the weld is being made.Instead, both processes have in effect accepted the weld characteristicsresulting from the speed and pressure initially selected.

It has been observed that the torque, heating rate and energy absorptioncharacteristics of the weld process have numerous points of contact withthe speed of rotation. For example, if the interface is heated to aplastic state and the speed of rotation then drops below a certain speedrange (which varies with different materials), the torque at theinterface will quickly increase by a substantial amount. The heatingrate has also been found to vary with the speed with which the parts arerotated.

The present invention utilizes the interrelationship between the speedand the other process characteristics in a novel way to achieve noveland continuous control of the process.

It is a primary object of the present invention to program the speed ofrelative rotation throughout the weld cycle in a way that can beparticularly suited to the specific parts and materials being welded. Itis a related object to use a drive mechanism which can function toproduce the desired variations in the speed, either up or down, at allstages in the welding process. It is a further object to combine withsuch a drive mechanism both a programmer which can be preset to generatethe desired speed versus time relationship and a controller which forcesthe output speed of the drive mechanism to follow that relationship.

The present invention permits continuous control and substantiallyinstantaneous change of the rotational speed throughout the weld cycle.As one result, the method and apparatus of the present invention can beemployed to produce the same speed pattern and the same weld zonecharacteristics as the inertial process. It is a specific object of thisinvention to be able to produce an inertial type of weld without the useof inertial weights.

The present invention is of course not limited to duplicating aninertial weld. It is more flexible in that it permits continuouscontrol, and variation, of the weld process. The rate at which the speedcan be changed and the range over which the speed can be varied areparticularly important features of the present invention. The speed canbe moved at will from a heating range of speeds to a forging range ofspeeds, and, where necessary, from the forging range back to the heatingrange. The present invention also permits staying in the forging rangefor as long as desired. A process and apparatus which permit these modesof operation constitute further specific objects of the presentinvention.

It is another object of the present invention to use a change of speedfrom fast to slow, and in some cases from slow to fast, to spread theheat pattern. The present invention thus does not rely only on thethcrmoconductivity of the materials to spread the heat.

In a preferred form of the present invention a variable speedhydrostatic transmission is used to drive the rotating part. Ahydrostatic transmission has comparatively low inherent inertia. Ahydrostatic transmission is also capable of a high response rate and canbe designed to develop whatever torques are required in the weldingprocess. A hydrostatic transmission will also develop maximum torques atminimum rotational speeds and therefor is a fortunate drive means forthe weld process in which high torques are required at low speeds. It isa further, specific object of the present invention to incorporate avariable speed hydrostatic transmission in the drive for a speedprogrammed welder.

In accordance with the present invention a speed programmer and acontroller are operatively associated in the control for the variablespeed hydrostatic transmission in a manner which permits continuous andeffective control throughout all parts of the weld process. A speedprogrammedwelding machine having a variable speed hydrostatictransmission and programmer and control as described constitutes afurther specific object of the present invention;

Other and further objects of the present invention will be apparent fromthe following description and claims and are illustrated in theaccompanying drawings which, by way of illustration, show preferredembodiments of the present invention and the principles thereof and whatare now considered to be the best modes contemplated for applying theseprinciples. Other embodiments of the invention embodying the same orequivalent principles may be used and structural changes may be made asdesired by those skilled in the art without departing from the presentinvention and the purview of the appended claims.

In the drawings:

FIG. 1 is a side elevation view, partly broken away to show details ofconstruction, of a speed programmed welder constructed in accordancewith one embodiment of the present invention;

FIG. 2 is a view like FIG. 1 showing a speed programmed welderconstructed in accordance with another embodiment of the presentinvention;

FIG. 3 is a schematic view of a hydraulic circuit for a speed programmedwelder constructed in accordance with a third embodiment of the presentinvention;

FIG. 4 is a side elevation view, partly broken away to show details ofconstruction, of a speed programmed welder like that shown in FIG. I buthaving inertial weights which can be connected in drive relation to thedrive shaft through a one way clutch to supply stored energy to the weldprocess to thereby extend the range of operation of the speed programmedwelder;

FIG. 5 is a schematic view of a control circuit for the machine shown inFIG. 1;

FIGS. 6A and 6B through FIGS. 10A and 10B are traces of weldcharacteristics developed in the course of weld operations performed bythe machine shown in FIG. 1;

FIG. 11 is a chart giving data relating to weld operations performed onthe machine shown in FIG. 1;

FIGS. 12 through 15 show typical speed-time curves that can be selectedand produced by the machine shown in FIG. 1;

FIG. 16 is a fragmentary view showing details ofa pressure programmingarrangement for the machine shown in FIG. 1; and

FIG. 17 is a schematic view of a hydraulic circuit incorporating arelief valve for controlling the amount of energy delivered to the weldinterface.

A speed programmed welding machine constructed in accordance with oneembodiment of the present invention is indicated generally by thereference numeral 21 in FIG.

The machine 21 includes a frame 22.

The two parts to be welded, workpieces WPI and WP2, are mounted withinchucks 23 and 24.

The chuck 24 does not rotate and is mounted on a fixture 26. The fixture26 is in turn mounted for axial movement on the machine frame 22 underthe control ofa load cylinder 27. A pressure programming circuit,- asshown in FIG. 16 and described in greater detail below, regulates thepressure in the load cylinder, and thus determines the force with whichthe parts WPl and WP2 are engaged.

The chuck 23 is mounted for rotation, but is not movable in an axialdirection.

The machine 21 includes variable speed drive means for rotating thechuck 23 and for changing the speed of rotation of the chuck 23 during aweld operation. In the embodiment shown in FIG. 1 the drive meansinclude an electric motor 28, a hydrostatic pump 29 and a hydrostaticmotor 31. The pump 29 is driven by the motor 28 and supplies pressurizedfluid to the motor 31 through a manifold 32. The hydrostatic motor 31drives the rotatable chuck 23 by a drive shaft 33.

The rotational speed of the motor 31 is determined by the angularposition ofa cam 34 in the motor and a cam 36 in the pump. Moving thecam 34 to increase the displacement of the motor 31 will, for any givenvolume of fluid supplied from the motor 29, decrease the rotationalspeed of the motor 31 and shaft 33. Moving the cam 36 to increase thedisplacement of the pump 29 will, for any given position of the cam 34in the motor 31, increase the rotational speed of the motor 31 and shaft33.

The position of the cam 34 is set by a hydraulically actuateddisplacement control 37. The position of the cam 36 is set by adisplacement control 38.

The machine 21 may also preferably include sensing units 39 and 41(rectilinear potentiometers in the machine illustrated in FIG. 1) forsensing the position of the cams 34 and 36. The sensing units 39 and 41serve as part of a feedback arrangement which will described below ingreater detail with reference to FIG. 5.

The machine 21 includes a tachometer generator 42 for generating asignal corresponding to the actual rotational speed in the shaft 33.This signal may be used in the feedback arrangement. It may also be usedin recording the actual speed.

The pressure programming control for the machine 21 referred to above isshown in FIG. 16 and is indicated generally by the reference numeral43.'The control 43 provides automatic regulation of the hydraulic fluidpressure supplied to the load cylinder 27 after the weld cycle isstarted.

The control 43 includes a timer 44, a comparator 46, a bias voltagesource 47, adjustable pressure relief valves 48 and 49, valves 51 and52, and solenoids 53 and S4 for controlling the positions of valves 51and 52.

The pressurized fluid for the cylinder 27 is supplied through a conduit56 by a pump which is not shown. A return conduit 57 leads to areservoir which is also not shown.

The timer is connected to the comparator 46 by a line 58 and isconnected to the solenoid 54 by a line 59.

The comparator is connected to the bias voltage source 47 by a line 61and is connected to the solenoid 53 by a line 62.

The valve 51 functions to change the inlet fluid pressure between thelevels determined by the adjustable pressure relief valves 48 and 49when the valve 51 is shifted between the number 1 and number 2 positionsshown in FIG. 16. This causes the load exerted by the load cylinder 27to vary accordingly.

In operation, as the start cycle button is pressed to initiate the weldcycle, the timer 44 functions to energize the solenoid 54 to switchvalve 52 to a position in which pressurized fluid from the inlet conduit56 is directed to the load cylinder 27. At this time valve 51 is in thenumber 1 position and the adjustable pressure relief valve 48 controlsthe pressure level to cause he load cylinder 27 to exert the desiredinitial load.

The timer 44 may be preset for any desired time interval to direct avoltage to comparator 46 which matches the bias voltage from the source47. When'this happens the comparator energizes solenoid 53 and switchesvalve 51 to the number 2 position. The inlet conduit 56 is thendisconnected from the adjustable pressure relief valve 49. In most casesthe valve 49 will be set for a higher pressure than the valve 48 so thatthe load exerted by the loading cylinder 27 will increase.

When the weld is completed the solenoid 54 is deenergized, and the valve52 is returned to a neutral position. This communicates the loadcylinder 27 with the return conduit 57 and permits the spring to retractthe piston of the load cylinder. The load cylinder 27 can also be adouble acting cylinder, and

' the valve 52 can be adapted to direct pressurized fluid to the rod endof the cylinder for returning the piston after the weld is completed.

The solenoid 53 is also deenergized at the end of the weld cycle, andthe spring 64 returns the valve 51 to the number 1 position illustrated.

The machine 21 includes speed programming means for selecting andproducing a predetermined variation of the rotational speed with time,that is, a desired speed versus time relationship, throughout the entirewelding period. The speed programming means are schematicallyillustrated in FIG. 5 and are indicated generally by the referencenumeral 71.

The means 71 include a programmer 72 and a controller 73.

The programmer 72 generates a desired speed signal and the controller 73forces the output speed of the shaft 33 to equal the programmed speed byapplying an appropriate torque to the parts being welded. In the formillustrated in FIG. 5 the programmer is electrical and includes a diodefunction generator and a time generator. While details of the circuitryof the programmer are covered in a separate application, it may be notedhere that the diode function generator approximates the desired speedversus time function by a series of straight line segments. The numberof segments usable in the presentation depends upon how exact the curvemust be fitted and the number of segments available. The diode functiongenerator has variable break points with adjustable slope. The breakpoint is the point of intersection between two straight line segmentscomprising a portion of the curve. The slope dials determine the slopeof each of the straight lines. The summation of the straight linesegments then approximates the function desired. The time generatorsweeps the diode function generator and provides the time axis for theprogram. The sweep rate or time axis during the reset and weld portionof the cycle are controlled by the reset sweep rate dial and weld sweeprate dial respectively. Other programming means, such as cam surfaces,tape or punched cards can also be used for generating the desired speedsignal.

The controller 73 includes electrohydraulic servo valves 74 and 76 whichcontrol the flow of pressurized fluid from a pump 77 through a conduit78 to the displacement controls 38 and 37. Valves 74 and 76 can alsocontrol the return flow of fluid through a conduit 79 from thedisplacement controls 38 and 37 to a tank 81.

The pump develops sufficient pressure in the control circuit to producerapid response of the displacement controls 37 and 38 to changes in thedesired speed setting. The speed signal from the programmer 72 issupplied to the servo valves 74 and 76 through lines 82 and 83. Thehydraulic circuit for actuating the displacement controls 37 and 38 alsoincludes a check valve 84 and an accumulator 86 downstream ofthe pump77.

The hydraulic circuit for the hydrostatic pump 29 and motor 31 includesa high pressure relief valve 87. In one form of the present inventionthe high pressure relief valve 87 was set to limit the maximum operatingpressure to 5,000 p.s.i. and the low pressure relief valve 88 was setfor 100 p.s.i.

The hydraulic circuit for the pump 29 and motor 31 also includes areplenishing pump 89 and a check valve 9! to replenish any system fluidlosses. This maintains a minimum inlet manifold pressure in the returnmanifold 32A to avoid cavitation of the pump 29.

The speed programming means 71 is a closed loop, active system whichincludes feedback means for comparing the actual speed with theprogrammed speed. The feedback means are effective to eliminatedifferences between the actual and the programmed speeds. These feedbackmeans include the rectilinear potentiometers 39 and 41 which sense theactual position of the earns 34 and 36. The feedback signals thusgenerated by the sensing units 39 and 41 are sent back to the programmerthrough lines 92 and 93. The desired speed and actual speed are comparedin the programmer and an appropriate signal is supplied to the servovalve 74 and servo valve 76 if any correction is required.

In the operation of the machine 21 thus far described the desired speedversus time relationship is first programmed into the programmer 72. Thespeed versus time curve might, for example, have a shape lie one of thecurves illustrated in FIGS. 12 through 15. The shape might also be likeone of the curves illustrated in the last vertical column of the chartshown in FIG. 11. Depending upon the particular parts and material to bewelded, the desired speed versus time curve might also have some otherparticular configuration which would be best suited for that particularweld. In any event the programming means 72 would be programmed toproduce that particular curve.

At the same time the pressure programming means 43 are programmed toproduce the desired pressure versus time relationship if something otherthan a constant pressure is desired.

The electric motor then accelerates the hydrostatic pump 29 and motor 31to the selected initial speed, and the load cylinder 27 shifts thefixture 26 and nonrotatable chuck 24, to the left as viewed in FIG. 1,to engage the parts WPl and WP2 in rubbing contact. In most cases, ifthe initial desired speed is relatively high, there will be a slightinitial departure of the actual speed from the desired speed (asindicated at 94 on the actual speed trace shown in FIG. 6A). This slightdeparture is quickly corrected, and for the rest of the weld cycle theactual speed corresponds quite closely with the desired speed.

In the machine 21 the control of the rotational speed of the shaft 33 isdivided between the displacement controls for the cam 34 and the cam 36.The cam 34 for the motor is held at a maximum angle for the speed rangeof zero to I500 r.p.m., and the angle of the pump can 36 is varied tocontrol the speed during this range. From 1500 rpm. to full speed (about3000 rpm. in one operating form of the machine shown in FIG. I) theangle of he pump cam 36 is held constant and the angle of the motor cam34 is varied.

FIG. 2 shows a machine which is generally like the machine shown in FIG.1 with the exception that the hydrostatic pump 29 and hydrostatic motor31 have been mounted in an end to end relationship to eliminate the needfor lengthy manifolds connecting the two units. In the modified machineshown in FIG. 2 a larger pump is used so that only a single displacementcontrol 38 is required to control the output speed of the shaft 33. Themotor 31 is a fixed displacement hydrostatic motor. The remainder of themachine 21 shown in FIG. 2 is substantially the same machine shown inFIG. 1.

The hydrostatic motor has relatively low inherent inertia and is capableof a high response rate so as to make it especially suitable as thedrive means for the speed programmed process.

The hydrostatic pump and motor combination can also be used as a braketo absorb excess energy in the event such small parts are to be weldedon the machine that even the low inherent inertia of the hydrostaticmotor would be excessive. In this event the braking is accomplished byreversing the displacement cam in the pump so that the motor acts as apump and the pump acts as the motor. The amount of energy absorbed bythe transmission in that mode of operation can be easily controlled byproviding an adjustable relief valve in the drive circuit. The energyrequired to blow the relief valve will be absorbed by the transmissionand the energy in excess of that required to blow the relief will beavailable to the weld interface for making the weld.

FIG. 17 shows a hydraulic circuit which permits controlled braking ofthe hydraulic motor. In the circuit shown in FIG. 17 an electric motor28 drives the variable displacement hydraulic pump 29. The pump 29supplies pressurized fluid through a manifold 32 to the hydraulic motor31. The hydraulic motor rotates the drive shaft 33 and spindle whichincludes the chuck 23. A. replenishing pump and valve group 89 suppliesmakeup fluid to compensate for that leaking from the circuit duringoperations.

The circuit shown in FIG. 17 also includes'a spool valve 90 which isconnected across the supply manifold 32 and return manifold 32A. Thespool valve is shiftable to one of the three positions illustrated by amanual valve positioner 100. The circuit also includes a variablepressure relief valve 95.

In operation, with the spool valve 90 in the number I position shown,the hydraulic motor 31 and the spindle may be accelerated by theelectric motor 28 and the variable displacement hydraulic pump 29 sincethe communication, through the valve 90, between the manifolds 32 and32A is blocked. When the spindle and chuck 23 reach the desired speedthe chuck and drive shaft 33 may be allowed to free wheel by moving thevalve 90 to the number 2 position. This places the manifolds 32 and 32Ain open communication and thus short circuits the drive circuit. Thepump 29 may be set to zero displacement at this time.

To use the transmission as a brake the valve 90 is moved in the number 3position. The motor'outlet conduit 32A is then in communication with themotor inlet conduit 32 by way of the variable pressure relief valve 95.The adjustment of the relief valve will then determine the amount ofenergy which is available to the weld to generate heat. That is, theenergy in the rotating drive shaft 33 spindle and chuck 23 required tocreate sufficient pressure to open the relief valve will be absorbed inthe transmission. The remainder of the energy in the rotatingcomponents, in excess of that required to open the relief valve, will beavailable to the weld to generate heat.

FIGS. 12 through 15 illustrate some typical speed time curves which canbe programmed into the speed programmed welder described above.

The generally parabolic shaped speed time curve shown in FIG. 12 ischaracteristic of an inertial weld using a relatively large flywheelrotating at a relatively low initial velocity. The rate of decay of theflywheel speed would be considerably slower than would be the case ifthe same amount of stored energy was stored in a smaller flywheelrotating at a high initial speed.

FIG. 14 shows a speed time curve which is typical of an inertial processin which the smaller flywheel is rotated at a higher initial speed. Bothof these speed time curves can be readily reproduced with the speedprogrammed welder described above.

As noted generally above in the introduction of this application,rotation of the parts to b welded above a certain range of speedsresults primarily in heating with little plastic working or forging, androtation of the parts below a certain range of speeds results primarilyin heavy plastic working or forging. As also noted above, the speedrange dividing the heating range from the forging range will vary withdifferent materials. It also is not sharply defined for any particularparts because of the velocity gradient across the radius of the rotatingparts. As the rotational speed of the parts is decreased the portion ofthe interface nearer the axis of rotation will go into the forging rangebefore the portions of the interface farther away from the axis ofrotation. Nevertheless, for any particular parts there is a band ofspeeds below which the torque increases appreciably so as to indicatethat the parts being welded are entering the forging range, and thisband of speeds is indicated generally by the broken line CS in each ofFIGS. 12 through 15. The critical speed range CS can also be illustratedas occurring at about the points indicated by the arrows CS on the speedcurve shown in FIG. 10A.

With continued reference to FIGS. 12 and 14 it can be seen thatoperation along the flatter speed curve shown in FIG. 12 will produce amore extended period of rotation in the forging range. In most casesthis is desirable and beneficial to the weld structure.

The speed range indicated by the line CS also represents the speed rangeat which a weld can form between the rotating parts if the interface hasbeen heated to a plastic state.

The continuously decreasing velocity curve illustrated in FIGS. 12 and14 may not be best suited for producing the required heating. In somecases a curve more like that shown in FIG. 13 is more effective and moreefficient. As illustrated in FIG. 13 the parts are rotated at arelatively constant high speed in the heating range and the speed isthen quickly dropped to a speed in the forging range. The amount offorging is then controlled by both speed and by the amount oftime theparts are rotated in the forging range.

As noted generally above, the heating of the interface can be influencednot only by the speed at which the parts are rotated but also byvariations in the speed at which the parts are rotated. A change inspeed does have the effect of spreading the heating radially across theinterface. This spreading effect can be particularly important whenparts of large diameter, and consequent large velocity gradients andlarge masses, are being welded. When large diameter bars are weldedthere can be problems in eliminating center defects. The areas of theinterface near the axis of rotation may not be heated sufficiently andmay not be worked sufficiently to fragment, disburse, and ejectinclusions which act as stress raisers. The speed time cycle illustratedin FIG. 15 has been found effective to minimize problems of centerdefects. In this cycle the parts are subjected to a period of heating,the parts are then subjected to forging, and the parts are thensubjected to an additional period of heating before a final forgingstep. The cycling back and forth between the heating and forging rangesproduces thermal and mechanical effects which are useful for weldingparts of large diameter.

It should be noted that the speed time cycle illustrated in FIG. 13could be produced by a planetary type of power shift transmissionprogrammed to shift under power from a high speed to a lower speed at apredetermined instant in the weld cycle. Such a machine could not ofcourse operate over the full range of speeds which can be produced bythe hydrostatic drive arrangement described above. Such a machine mighthowever have utility for high volume production of one particular kindof welded article. FIGS. 6A through 108 are traces of processcharacteristics as recorded during specific weld operations performedwith the machine shown' in FIG. 1. These traces show the versatility ofthe speed programmed welder. In each figure the actual speed and thepressure and torque are shown in the A view while the desired speed,energy and horsepower traces are shown in the B view. These traces wereseparated in two different views to make the traces easier to follow.

The first five horizontal data lines of FIG. 11 correspond respectivelyto FIGS. 6 through 10.

With a specific reference now to FIGS. 6A and 6B, the weld processoperation from which these traces were taken included engagement of theparts at a relatively high initial speed, followed by reduction to alower speed and a period of heating at this second speed, a reduction toa second lower speed within the forging range and an extended period ofconstant speed rotation in the forging range.

The weld operation from which the traces of FIGS. 7A and 78 were takenincluded engagement of the parts at a very low initial rotational speed.The speed was then increased to a speed well within the heating rangeand was maintained at that level until the required amount of heatinghad been produced.

. there is almost no problem of stalling at the start. This mode ofoperation can also be advantageously combined with a gradual buildup inthe axial load to limit the power which is consumed in the initial partof the weld cycle and also to minimize the initial torque. This kind ofprogrammed speed cycle 'can also help prolong the machine life since thebearings are not subject to high load at high speeds as is the case inmost other weld cycles where the parts are initially engaged at arelatively high speed and under a substantial load.

The speed and the load can thus be programmed independently of oneanother (for example, the speed can be increased while the load isdecreased) to avoid excessive torques or extremely low torques and tomaintain a uniformly high power input. FIGS. 8 and 9 indicate that thespeed programmed welder can be programmed to produce substantially thesame constant speed as conventional friction welding. In the weldoperation shown in FIGS. 8A and 8B, however, the total process time wassomewhat shorter than would normally be used in conventional frictionwelding.

The traces shown in FIGS. 9A and 98 were taken from a weld operationwhich simulated an inertial weld in which the flywheel speedcontinuously decreases.

In the weld operation shown in FIGS. 10A and 108 the programmer wasprogrammed to continuously decrease the speed to a speed below thecritical range and into an area of heavy plastic working. Then the speedwas increased to a level where heating, rather than forging,predominated. Note the lower torque. The speed was then decreased againto the forging range before rotation was ended. This kind of cycle, asnoted above, can have specific advantages in eliminating center defects.

The XCO material noted in the sixth horizontal data line of the chartshown in FIG. 11 is a very high carbom very high alloy valve materialwhich has extreme resistence to temperature, seizing, scufiing andwelding. This material was successfully welded under the conditionsindicated in FIG. 11 by using a stepped pressure cycle in which'thehigher pressure was applied at about the point indicated by the verticalline on the speed curve in FIG. 11. This material has been found to bedifficult to weld by the inertial process. The total energy and averagehorsepower columns are blank for the XCO weld because these quantitieswere not recorded for this particular weld operation.

In some instances it may be desirable to extend the range of aparticular size of welding machine beyond the maximum output torque ofthe hydrostatic motor. Thus, in some instances it may be desirable touse a smaller size hydrostatic motor and a supplementary drivearrangement for supplying driving torque in excess of that which can besupplied by the hydrostatic motor, rather than to use a largerhydrostatic motor having the necessary maximum torque output. FIG. 4shows a speed programmed welder with a supplemental flywheel. In FIG. 4the speed programmed welder is generally like that shown in FIG. 1except for the addition of the supplemental flywheel 101.

The flywheel 101 is mounted on a carrier 107. The carrier is mounted forrotation on the shaft 33 by bearings 102. The flywheel 101 is alsoadapted to be connected to drive the shaft 33, under certain conditionsof operation to be described below, by a one-way clutch 103.

A collar l04 is spline connected to the shaft 33 so as to be axiallyshiftable on the shaft. The collar 104 has a friction facing 106. Whenthe friction facing is pressed into engagement with' the flywheelcarrier 107 the carrier and the flywheel rotate with the shaft 33. Ahydraulic cylinder 108 shifts the splined collar 104 to engage thefriction face with the flywheel carrier or to disengage the frictionfacing from the flywheel carrier.

1n operation, the cylinder 108 is actuated to clutch the splined collar104 to the flywheel carrier 107 during a portion of the time that theshaft 33 is being accelerated to the desired initial rotational speedprior to engagement of the parts Wll and WP2. This causes the flywheelto be accelerated, and when the desired amount of inertial energy hasbeen stored in the flywheel, the splined collar 104 is shifted todisconnect the flywheel 101 from the shaft 33. The flywheel thenfreewheels on the shaft 33 while the shaft 33, and chuck 23, areaccelerated to the desired speed at which the parts are to be initiallyengaged.

The parts WPl and WP2 are then engaged in rubbing contact. By properlycontrolling the pressure of engagement the maximum torque in the initialstage of the weld process can be maintained well within the capacity ofthe hydrostatic motor 31. However, as the speed is dropped into theforging range, higher torques will be produced, and it is during thisphase of operation that the stored energy of the flywheel is used tosupplement the torque output of the hydrostatic motor.

As the rotational speed of the shaft 33 drops below the speed at whichthe flywheel is rotating, the one-way clutch 103 connects the flywheelin drive relation with the shaft 33. The energy stored in the flywheelthen assists the hydrostatic transmission in driving the rotating partsthrough the forging phase of the weld cycle.

FIG. 3 is a schematic view of another form of hydraulic drive for aspeed programmed welding machine. In FIG. 3 a fixed displacement pump111, driven by an electric motor or an internal combustion engine whichis not shown, supplies pressurized fluid to a hydraulic motor 112through a conduit 113.

The motor 112 drives an output shaft, like the output shaft 33 of themachine shown in FIG. 1.

The speed of the motor 112 is determined by the amount of hydraulicfluid supplied through an electrohydraulic servo valve 114. The positionof the modulating valve 114 is controlled by a summingjunction 116.

The desired speed signal is generated in a programmer 72, and thisdesired speed signal is supplied to the summing junction .through a line117. The actual speed signal is also supplied to the summingjunctionfrom a tachometer 42 through a line 118. Any difference in the desiredand actual speed signals is supplied to the valve 114 through a line 119to cause the valve to move in the proper direction to increase ordecrease the flow of hydraulic fluid to the motor 112.

In some conditions of operation the valve 114 may be shifted to theextreme right to tend to drive the motor 112 in reverse and to thereforcause the motor 112 to act as a brake.

The conduit 113 also contains a filter 121, a check valve 122 and anaccumulator 123. The accumulator stores pressurized fluid for periods ofoperation when the drive requirements of the motor require more fluidthan can be supplied by the pump 111. A bypass valve 124 is operative tobypass excess pump output when the accumulator has been fully chargedand the flow requirements of the motor are less than the output of thepump.

The drive arrangement shown in FIG. 3 also includes means for effectinga rapid disconnect of the drive from the part being rotated. These meansinclude a solenoid actuated dump valve 124. A pressure switch 126 isoperatively connected to the solenoid to dump the pressure, and the flowof fluid from the input of the motor 112, when he pressure reaches thepredetermined value determined by the switch 126. If the pressure switch126 is set for a sufficiently low pressure, the switch will disconnectthe motor from driving relation with the part being rotated at somepoint in the final torque rise near the end of the weld process. Thisnormally would not be desired since it would eliminate much oftheforging. However, in some particular application this mode of operationmight be useful to minimize the overall cycle time for a weldingoperation.

While we have illustrated and described the preferred embodiments of ourinvention, it is to be understood that these are capable of variationand modification, and we therefore do not wish to be limited to theprecise details set forth, but desire to avail ourselves of such changesand alterations as fall within the purview of the following claims.

We claim:

1. A machine for welding workpieces by rotating the workpieces inrubbing contact at a common interface to develop weld heat by frictionand plastic working, said machine comprising, loading means for pressingthe workpieces together at the interface, variable speed drive means forrotating one workpiece with respect to the other to produce the rubbingcontact and a plastic condition at the interface, and speed programmingmeans for selecting and producing a predetermined variation of therotational speed with time throughout the entire welding period, saidspeed programming means including a programmer for generating a desiredspeed signal and a controller for producing an actual speed inaccordance with the desired speed signal.

2. A machine as defined in claim 1 wherein the drive means include avariable speed hydrostatic motor.

3. A machine as defined in claim 2 wherein the speed programming meansinclude a variable angle cam in the hydrostatic motor and a control forvarying the angle of inclination of the cam.

4. A machine as defined in claim 1 wherein the drive means include avariable speed hydrostatic pump and motor combination and wherein thespeed programming means include a variable angle cam in the hydrostaticpump and motor combination for varying the speed ratio across the pumpand motor combination.

5. A machine as defined in claim 4 including a control for varying theangle of the cam and wherein the control for varying the angleofinclination of the cam is movable to a position in which thehydrostatic motor acts as a brake to slow rotatron.

6. A machine as defined in claim 1 wherein the speed programming meansinclude feedback means for comparing the actual speed with theprogrammed speed and effective to eliminate differences between theactual and the programmed speeds.

7. A machine as defined in claim 1 wherein the speed programming meansand the drive means are operatively associated so as to produce plasticworking at low speeds while the bond zone is in a forgeable conditionjust as the weld period terminates.

8. A machine as defined in claim 1 wherein the speed programming meansinclude a servomechanism associated with the drive means, and anelectrical function generator and a time generator for supplying thedesired speed signal to the servomechanism.

9. A machine as defined in claim 1 including a rotatable flywheel andmeans for selectively connecting the flywheel to the drive means to takestored energy from the rotating flywheel during a portion of the weldcycle.

10. A machine as defined in claim 9 wherein the connecting means includea one-way clutch effective to connect the flywheel to the drive means indrive relationship when the rotational speed of the drive meansdecreases to a predetermined speed.

11. A machine as defined in claim 1 wherein the drive means include apower shift transmission for changing the speed or rotation while underpower.

12. A machine as defined in claim 1 including pressure programming meansfor selecting and producing a predetermined variation of the loadapplied by the loading means throughout the entire welding cycle.

13. A machine as defined in claim 1 wherein the drive means include ahydraulic pump and motor and wherein the motor than can be supplied fromthe pump.

15. A machine as defined in claim 13 including a dump valve associatedwith the hydraulic motor for bypassing the flow of pressurized fluidaround the motor to discontinue the drive to the workpiece.

1. A machine for welding workpieces by rotating the workpieces inrubbing contact at a common interface to develop weld heat by frictionand plastic working, said machine comprising, loading means for pressingthe workpieces together at the interface, variable speed drive means forrotating one workpiece with respect to the other to produce the rubbingcontact and a plastic condition at the interface, and speed programmingmeans for selecting and producing a predetermined variation of therotational speed with time throughout the entire welding period, saidspeed programming means including a programmer for generating a desiredspeed signal and a controller for producing an actual speed inaccordance with the desired speed signal.
 2. A machine as defined inclaim 1 wherein the drive means include a variable speed hydrostaticmotor.
 3. A machine as defined in claim 2 wherein the speed programmingmeans include a variable angle cam in the hydrostatic motor and acontrol for varying the angle of inclination of the cam.
 4. A machine asdefined in claim 1 wherein the drive means include a variable speedhydrostatic pump and motor combination and wherein the speed programmingmeans include a variable angle cam in the hydrostatic pump and motorcombination for varying the speed ratio across the pump and motorcombination.
 5. A machine as defined in claim 4 including a control forvarying the angle of the cam and wherein the control for varying theangle of inclination of the cam is movable to a position in which thehydrostatic motor acts as a brake to slow rotation.
 6. A machine asdefined in claim 1 wherein the speed programming means include feedbackmeans for comparing the actual speed with the programmed speed andeffective to eliminate differences between the actual and the programmedspeeds.
 7. A machine as defined in claim 1 wherein the speed programmingmeans and the drive means are operatively associated so as to produceplastic working at low speeds while the bond zone is in a forgeablecondition just as the weld period terminates.
 8. A machine as defined inclaim 1 wherein the speed programming means include a servomechanismassociated with the drive means, and an electrical function generatorand a time generator for supplying the desired speed signal to theservomechanism.
 9. A machine as defined in claim 1 including a rotatableflywheel and means for selectively connecting the flywheel to the drivemeans to take stored energy from the rotating flywheel during a portionof the weld cycle.
 10. A machine as defined in claim 9 wherein theconnecting means include a one-way clutch effective to connect theflywheel to the drive means in drive relationship when the rotationalspeed of the drive means decreases to a predetermined speed.
 11. Amachine as defined in claim 1 wherein the drive means include a powershift transmission for changing the speed or rotation while under power.12. A machine as defined in claim 1 including pressure programming meansfor selecting and producing a predetermined variation of the loadapplied by the loading means throughout the entire welding cycle.
 13. Amachine as defined in claim 1 wherein the drive means include ahydraulic pump and motor and wherein the speed programming means includea modulating valve associated with the motor for controlling the speedof the motor. 14 A machine as defined in claim 13 including anaccumulator between the pump and motor for storing pressurized hydraulicfluid from the pump for supply to the motor during periods when the weldcycle requires more work from the motor than can be supplied from thepump.
 15. A machine as defined in claim 13 including a dump valveassociated with the hydraulic motor for bypassing the flow ofpressurized fluid around the motor to discontinue the drive to theworkpiece.